The present invention relates to a sealed construction for a sealed battery that uses a battery case reinforcing plate, and to a method for manufacturing the same.
The rapidly increasing use in recent years of power supplies for portable and cordless AV equipment, personal computers, portable communication devices, and other devices is driving research into making smaller and higher capacity non-aqueous electrolyte secondary batteries, such as high-capacity alkali storage batteries and lithium ion secondary batteries.
A battery sealing work procedure disclosed in Japanese Published Unexamined Patent Application (Kokai) 58-112259 is described hereafter.
FIG. 4 shows the construction of a conventional sealed battery. In FIG. 4, 1 is a battery case that also functions as a terminal plate, 2 is a plastic insulation gasket, 3 is a metal reinforcing plate that prevents deformation, such as denting or bulging, of the battery case, 4 is a metal cap that also functions as one of the battery terminals, and 5 is a sealing member in which an anti-explosion mechanism is incorporated.
After electricity-generating elements 6 are placed into the battery case 1, the reinforcing plate 3 is placed at a specified position from the opening of the battery case 1 and then fixed in place using laser welding or another method. Next, a drawing die of a specified shape is used to gradually draw the circumference of the battery case 1 inward at a location closer to the opening than the fixed position of the reinforcing plate 3 and to form a circumscribing indentation 7 around the circumference. The indentation 7 is for supporting from beneath the plastic insulation gasket 2 and the sealing member 5. After the inside surface of the battery case 1 from the above-mentioned indentation 7 to the edge of the opening is coated with a sealant such as blown asphalt, the plastic insulation gasket 2, which has been previously coated on the inside with blown asphalt, and the above-mentioned sealing member 5 are placed on the indentation 7, and the edge 1a of the battery case 1 is compression-formed and sealed by a crimping die while the above-mentioned indentation 7 is preserved.
In the above sealed battery, however, the indentation 7 is provided in the battery case 1 using a drawing process to provide a resting place for the plastic insulation gasket 2 and the sealing member 5, as well as to mitigate the compression pressure that is applied when the battery case 1 is crimped. This reduces the effective capacity of the battery case 1, which makes it difficult to achieve high electric capacity.
It is also difficult to form the above-mentioned indentation 7 with stability, which means that the surface on which the plastic insulation gasket 2 and the sealing member 5 are rested is not necessarily completely flat at all times, causing problems such as deformation of the reinforcing plate 3 or creating a non-uniform shape during crimping. This also makes it difficult to avoid defects that allow the sealed electrolyte to leak out.